Vulnerability Description
A vulnerability in huggingface/transformers versions <=5.8.0.dev0 allows an attacker to perform arbitrary file writes via path traversal. The issue resides in the `save_pretrained()` methods of `PreTrainedTokenizerBase` and `ProcessorMixin`, where keys from the `chat_template` dictionary are used directly as filenames without proper validation. An attacker can exploit this by publishing a malicious Hugging Face Hub repository with a crafted `tokenizer_config.json` file. When a victim downloads and saves the tokenizer or processor, the attacker-controlled keys can escape the intended save directory, enabling arbitrary file writes with attacker-controlled content. This vulnerability affects multiple processors inheriting from `ProcessorMixin`, including Idefics, Florence, Gemma, Phi, and Qwen-VL.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/huggingface/transformers/commit/eaaaf8494dd5386634ae37d1d1222
- https://huntr.com/bounties/362824d5-fe18-40e8-a6cf-62277f97a170
FAQ
What is CVE-2026-9856?
CVE-2026-9856 is a vulnerability with a CVSS score of 7.1 (HIGH). A vulnerability in huggingface/transformers versions <=5.8.0.dev0 allows an attacker to perform arbitrary file writes via path traversal. The issue resides in the `save_pretrained()` methods of `PreTr...
How severe is CVE-2026-9856?
CVE-2026-9856 has been rated HIGH with a CVSS base score of 7.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-9856?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.